The invention relates to a process for preparing self-binding pigment particle suspensions, to a self-binding pigment particle suspension as well as to a paper product comprising self-binding pigment particles and to the use of the self-binding pigment particle suspension as filler material.
Mineral materials and binders are among the main constituents used in the manufacture of numerous products such as paints, paper and plastic materials. Therein, mineral materials such as calcium carbonate and other particulate materials contribute mechanical and optical properties, while the binder, generally latex-based and in the form of aqueous suspensions or dispersions, provide the necessary adhesion and cohesion for the respective constituents of the end product to be produced.
In order to avoid the logistic difficulties of handling mineral materials and binders separately, and further to avoid the unwanted physical and chemical interactions developed in comparable mixtures of mineral materials and binders, self-binding pigment particles have been developed and are known to industry. In this regard, self-binding pigment particles contributing both the properties of the mineral material and of the binder may be directly implemented in a variety of applications. This unique product named self-binding pigment particles refers to distinct, solid particles, formed of mineral material and binder that are intimately bound to one another. The internal cohesion forces are such as to provide the self-binding pigment particles with excellent mechanical stability.
Self-binding pigment particles are prepared by a process implementing at least one step of grinding mineral materials in the presence of binder, where grinding refers to an operation leading to a reduction in the particle size; the mineral materials in the self-binding pigment particles have a smaller diameter than the initial mineral material used to produce them. Such self-binding pigment particles are described in a number of documents, including WO 2006/008657, WO 2006/128814, and WO 2008/139292.
However, there is still a need in the art for a process for preparing self-binding pigment particle suspensions which would solve one or more of the following multifaceted technical problems:                to prepare a suspension of self-binding pigment particles resulting in a paper coating having a content of binder that is below the content of latex binder typically used in the preparation of such paper coatings;        to prepare a suspension of self-binding pigment particles allowing for the provision of a filler material for paper products such that the paper product has a sufficient tensile index, preferably a tensile index of at least 10 Nm/g;        to prepare a suspension of self-binding pigment particles such that the content of components based on fossil resources in the obtained suspension is reduced, that is to say the self-binding pigment particle suspension comprises a binder that is obtained from renewable resources;        to prepare a suspension of self-binding pigment particles such that the obtained suspension provides a higher biodegradability than a corresponding suspension prepared with latex-based binder typically used in the preparation of such a suspension;        to prepare a suspension of self-binding pigment particles having a sufficient microbiological stability such that a fouling of the obtained suspension and end products prepared from such a suspension is delayed;        to prepare a suspension of self-binding pigment particles containing less sticky materials such that less deposits are observed on the equipment used during preparation, storage and application of the suspension, that is to say a suspension that provides a better handling.        
There is a continuous need for improving processes for the preparation of self-binding pigment particle suspensions which addresses the foregoing technical problems described and especially allows for reducing the content of polymeric latex-based binder in such suspensions.